<script>
      
    // es6 之前 
    var name = 'a';

    // es6 开始 
    let a = 'aa';
    const b = 'bb';
    console.log(a);
    console.log(b);
    
    console.log('-----------------');
  
    let res = `${a}`+'---'+`${b}`;
    console.log(res);


  </script>